Article II — MINIMUM REQUIREMENTS

328.1-5. Runoff Design.

Storm water runoff from a subdivision shall be collected and conveyed by a drainage system approved by the Director of Public Works. Maximum runoff shall be computed using the Rational Method. The Rainfall Intensity - Duration Curve, for Eureka, and “C” values approved by the Director of Public Works shall be used in computation. Runoff design shall accommodate the full and anticipated future development within the drainage area. In cases

The Humboldt County Code is current through Ordinance 2784, passed March 10, 2026.

Page 905 of 1183

Title III Land Use and Development | Humboldt County Code

where the drainage areas are undeveloped, fully improved conditions shall be determined by the designation of the area on the General plan or the zoning classification of the area. The drainage system shall provide for the protection of the abutting properties that would be adversely affected by any increase in runoff attributed to the development, for which off-site storm drain improvements may be required. (Ord. 1758, § 1, 11/12/1986)

328.1-6. Protection from Surface Waters.

All portions of building sites shall be protected from flood hazard, inundation, sheet flow and ponding of storm waters, springs and all other surface waters. All finished floors shall be a minimum of one foot above the water surface of a 100-year frequency storm runoff. (Ord. 1758, § 1, 11/12/1986)

328.1-7. Adequate Storm Drainage Facilities.

(a) The design of all improvements on any parcel within the McKinleyville Drainage Area shall be such that all surface waters occurring within the parcels, as well as all surface waters flowing onto and/or through the parcel shall be conveyed through the parcel without damage to any improvement, building site, or dwelling which may be constructed on the parcel or on any other parcels in the vicinity. Drainage facilities for any improvement shall be designed to adequately convey the storm water runoff from the ultimate development of the drainage basin or watershed. (Ord. 1758, § 1, 11/12/1986)

(b) Site development shall be accomplished wherever possible in a manner that will maximize percolation and infiltration of precipitation into the ground and will minimize direct surface runoff into adjoining streets, water courses, or properties. (Ord. 1758, § 1, 11/12/1986)

(c) Site development shall be accomplished wherever possible in a manner to maximize use of natural drainage features. (Ord. 1758, § 1, 11/12/1986)

328.1-8. Surface Water Flowing from a Subdivision.

Surface water flowing from a parcel or subdivision in any form or manner shall be conveyed without damage to any improvement, building, or dwelling both within and downstream of the subdivision to a natural watercourse having a definable bed and banks, or to an existing adequate storm drainage facility. Storm drainage facilities to be constructed outside of the parcel or subdivision shall be designed to adequately convey the storm water runoff from the ultimate development of the drainage basin or watershed lying within and above the subdivision. Any surface waters detained or ponded on adjacent property(s) as the result of improvements constructed by the developer or subdivider, shall not cause any damage to said property. (Ord. 1758, § 1, 11/12/1986)

The Humboldt County Code is current through Ordinance 2784, passed March 10, 2026.

Page 906 of 1183

Title III Land Use and Development | Humboldt County Code

328.1-9. Storm Water Disposal Restriction.

Storm water flowing from a parcel or subdivision in any form or manner shall not be permitted to flow into any sanitary sewer or any other facility not specifically intended for storm water runoff. (Ord. 1758, § 1, 11/12/1986)

328.1-10. Capacity of Channels and Conduits.

Drainage channels and conduits shall have the following minimum capacities: (Ord. 1758, § 1, 11/12/86)

(1) Major Drainage Channels. Major drainage channels and conduits shall have sufficient capacity to contain a 100-year frequency or occurrence runoff. (Ord. 1758, § 1, 11/12/1986)

(2) Secondary Drainage Channels. Secondary drainage channels and conduits shall have sufficient capacity to contain a ten-year frequency of occurrence runoff, as well as sufficient additional capacity so that floodwaters escaping therefrom shall not reach an elevation within one foot of any dwelling or commercial structure. (Ord. 1758, § 1, 11/12/1986)

(3) Minor Drainage Channels. Minor drainage channels, conduits, and appurtenant facilities shall have sufficient capacity to contain a ten-year frequency of occurrence runoff, as well as sufficient additional capacity so that floodwaters escaping therefrom shall not reach an elevation within one foot of any dwelling or commercial structure. (Ord. 1758, § 1, 11/12/1986)

328.1-11. Facilities Design Criteria.

Drainage systems shall conform to the requirements contained in Section 4, “Drainage” of the Humboldt County Roadway Design Manual adopted by the Board of Supervisors on February 1, 1972, as it may be amended from time to time. (Ord. 1758, § 1, 11/12/1986)

328.1-12. Easements.

Necessary easement to construct and maintain drainage facilities shall be required. The Director of Public Works, following accepted engineering practices, shall set the widths of these easements as developments warrant, and he is encouraged, consistent with accepted engineering criteria, to make them the minimum size necessary to plan for the ultimate development of McKinleyville. (Ord. 1758, § 1, 11/12/1986)

The Humboldt County Code is current through Ordinance 2784, passed March 10, 2026.

Page 907 of 1183

Title III Land Use and Development | Humboldt County Code